LCR meter: what is it and what is it used for?

It so happens that radio amateurs most often use three basic instruments: a voltmeter, an ammeter, and an ohmmeter. But sometimes a job calls for a more complex and less common instrument: an LCR meter.
Of course, these instruments come in both professional and "hobbyist" versions. But first, let's look at what an LCR meter actually is.

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As the name suggests, the instrument measures three basic quantities:
L - Inductance
C - Capacitance
R - Resistance

Of course, most modern multimeters can measure capacitance and resistance, but LCR meters usually do so more accurately and over a wider range. They can also make additional measurements, such as Q factor, dissipation factor, and ESR (equivalent series resistance), and take these measurements at different frequencies.
This functionality is needed when ordinary multimeters are no longer enough, for example, when troubleshooting switch-mode power supplies, voltage converters, and RF circuits.

Typical examples:
1. Resistors, the most common type of electronic component.


Common resistance values are no problem, but measuring low-value resistors can be more challenging. A regular multimeter can often measure resistances of around 1-2 Ω and above accurately enough. Below that, lead and probe resistance, along with limited resolution, starts to have a significant effect. Even the fairly accurate Uni-T 61E has a resolution of just 10 mΩ in this mode, while even an inexpensive LCR meter has a minimum resolution of 0.1 mΩ.
So while a multimeter can measure resistors from 0.05-0.1 Ω with reasonable accuracy, at 10 mΩ it can no longer measure anything reliably. Below are measurements of two resistors rated at 1 and 2.2 mΩ for comparison.




Measuring low resistances is often necessary when checking, selecting, or making current-sense shunts. An alternative is to measure the voltage drop, but that requires an adjustable power supply, an ammeter, and a voltmeter.


The ability to measure low resistances is also useful for spotting problems such as incorrect markings, especially on low-value resistors.
The resistor on the left is marked 0.1 Ω, and the one on the right 0.22 Ω, but their actual resistance is almost the same. Errors like this can sometimes be very costly.


Measuring low resistance can also help determine whether MOSFETs are genuine. Counterfeit and remarked transistors have been appearing on the market more and more often lately. Simply measuring their on-state resistance doesn't give you the full picture, but it does let you quickly see what you're dealing with.
For this test, all you need besides the instrument is a 9 V battery. Datasheet values are usually specified at a gate voltage of 10 V, but that isn't important here. Also, the drain-source resistance should ideally be measured under load, at the current usually specified in the datasheet, but that requires at least a bench power supply.
To test a transistor, connect the test probes to the drain and source leads (usually the middle and right ones), then apply 9 V to the outer leads. You don't need to keep the voltage applied; charging the gate capacitance is enough. Be careful not to accidentally connect the battery to the instrument's probes. You can even "charge" the transistor first and connect the probes afterward.


2. Capacitors are used somewhat less often, but they have their own quirks. Unlike resistors, for example, they are much more prone to aging, especially electrolytic capacitors in switch-mode power supplies, motherboard voltage converters, and similar circuits.


A capacitor's ESR is particularly important. Sometimes a capacitor dries out without losing much capacitance, but its internal resistance increases significantly.
A regular multimeter won't detect this. You could replace everything, but that's not always convenient and can often be difficult or expensive. Also, LCR meters often let you take measurements without desoldering the component, although this depends on how it's connected in the circuit.

1. Most multimeters measure a capacitor as an ideal component, without accounting for its characteristics. Sometimes that's enough; sometimes it isn't.
2. More advanced instruments can separate the capacitor itself from its internal resistance and measure these parameters individually.
3. In reality, the equivalent circuit of a capacitor is much more complex, and all these parameters can also be measured. But that requires a completely different class of instrument, which ordinary electronics hobbyists usually don't need.


As an example, here's a comparison of two capacitors: a cheap Chinese one and a name-brand one. Even an accurate but otherwise ordinary multimeter considers them almost identical, showing only a small difference in capacitance. But connect them to an LCR meter and you'll see that their internal resistance differs by almost a factor of 5! If you plan to use capacitors in switching power supplies, this difference in resistance will affect both heating—and therefore service life—and the power supply's performance. Capacitors with high internal resistance can't effectively suppress spikes.



3. Inductors, transformers, and other wound components are even harder to test than capacitors and resistors, and few multimeters can measure inductance at all.


An LCR meter makes it easier to wind coils and transformers, and to find shorted turns. By comparing a component with a known-good one or a known value, you can easily tell that a transformer or inductor is faulty: its inductance will have changed significantly.


There are special instruments for finding shorted turns, but an LCR meter can also identify the problem. For example, the transformer on the left is good; the one on the right is the same transformer, but with one turn shorted. You can see that the winding's inductance has dropped substantially. The shorted turn also affects the measured DC resistance of the winding.


Let's look at a few meters in different price ranges and their pros and cons.

First, of course, the famous Marcus transistor tester. It comes in a wide range of versions, with or without an enclosure, in basic versions or with a frequency counter and zener diode testing, and as both DIY and factory-built units. It's sometimes mistakenly called an ESR meter, which isn't quite right: it was originally designed as a transistor tester, and ESR measurement was just one of its functions, added much later.
There's also a large community around this device on the well-known vrtp site, where you can find out how to flash the transistor tester.
I have two DIY versions of my own, and one of them can test zener diodes, check quartz resonators, and so on.


For a beginner, this is probably a great option. The tester can measure a wide variety of components. It's especially handy for testing transistors—for example, figuring out which lead is the base, emitter, or collector—but it also does a perfectly good job with capacitors and resistors.


More importantly, this tester can measure capacitance and inductance, and perform complex measurements too. For example, it can show not just an inductor's inductance, but also the winding's DC resistance. Likewise, for capacitors it measures not only capacitance, but also internal resistance (ESR).
There are some drawbacks, of course. Its simple circuit design and two-wire connection make it difficult to measure low resistances.


A kind of hybrid transistor tester and oscilloscope from Fnirsi has recently appeared. I haven't tried it myself, but judging by the number of orders, it's popular.



Next up are more specialized devices: LCR meters. They can't test transistor parameters, but they measure inductance and low resistance better than a universal tester, for example. A typical example is the LC100-A.
Unlike the previous device, the ESR tester's firmware is closed-source, so it can't be updated.


There are other similar meters, but unfortunately they retain one drawback of universal testers: a two-wire connection. This means the measurement can be strongly affected by contact quality and lead length. Calibrating the ESR tester helps compensate for lead length, of course, but it's better to use short, thick leads.


For more experienced users, there's a meter that may not be professional-grade, but is certainly close to it. In addition to standard measurements, it can perform complex measurements and measure quality factor and dielectric loss. The instrument also has a four-wire connection.
It can also take measurements at three frequencies: 100 Hz, 1 kHz, and 7.8 kHz.

This instrument is sold both as a kit for assembly and as a fully assembled unit. I have a detailed review of the instrument and the assembly process.


The instrument can automatically select the quantity to measure, or you can select it manually. Manual mode is preferable, since the automatic mode sometimes misidentifies the component type.


The four-wire connection immediately puts the XJW01 head and shoulders above many other hobbyist instruments. This connection separates the current-source circuit from the measurement circuit, so lead length and contact resistance no longer affect the measurement results.
This type of connection is used in almost all professional instruments, I think. Even when the component plugs directly into the instrument's terminals, a special contact assembly with four contacts is used.


Special clips, tweezers, and remote contact fixtures are used to connect the components under test. Since they also use BNC connectors, even branded accessories are compatible with the XJW01 shown above.


You get essentially the same features in branded but relatively affordable LCR meters from Uni-T and Hantek. They also have four-wire connections and can measure capacitance, inductance, and resistance, including ESR, as well as complex quantities.
Modern instruments often measure at frequencies up to 100 kHz, allowing components to be tested at a higher level. This can be especially useful when selecting capacitors for modern switching power supplies, which operate at comparable frequencies.


It's also worth mentioning instruments that could be considered entry-level professional models, such as the ET4401
It's an interesting instrument; maybe I'll try it out sometime.



But be careful: there are many similar LCR meters for sale, and they often claim a frequency range of up to 100 kHz. However, if you read the manual carefully, you'll see that the maximum capacitance measurable at that frequency is significantly lower. For example, according to the manual for the DT9935, it can measure up to 200 µF at 10 kHz, but only up to 2 µF at 100 kHz.


Beyond that, you get into professional-grade instruments, which are usually too expensive for the average user. In many ways, they're similar to the ones shown above and often use the same measurement principle, but their components, features, computer connectivity, and especially their calibration options put them in a completely different class. Of course, they're beyond the scope of this article, but it wouldn't be right to leave them out entirely. The photo shows a Rohde & Schwarz HM8118 LCR meter, with a specified measurement error of 0.05–0.5% (the XJW01 is specified at 0.3–0.5%) and a price of around $3000.
Its features include measurements at frequencies up to 200 kHz, up to 12 measurements per second, and an external capacitor bias voltage of up to 40 V.



To sum up, an ordinary transistor tester is more than enough for a beginner electronics hobbyist, covering 90% of their needs. More experienced users will probably need a more capable instrument, and can choose either a ready-made model from a mid-range brand or a kit like the XJW01. Professionals, on the other hand, may need more than just an instrument: they may need one listed in the state register, so that they can order official metrological verification for it. This is another distinction between professional and hobbyist instruments, even high-quality ones.